It probably took decades to get to your current body weight. Should it not then take at least 5 years to get back to your target weight ? True the caloric math shows you could probably get to 250lbs in a year with a 600-800 a day diet. But can any human actually stick with that diet for more than a month ? If not, you would be better eating 1600-1800 a day if you could stick with it for a year.
As an aside, at times I wonder if our obesity epidemic is in part related to an ever increasing target/acceptable weight. When I was a kid, if you could pinch an inch, you were overweight (I stop drinking calories if I pass the threshold). Even my childhood bathroom scale maxed out at 250 which implied that 250 must be extreme morbid obesity.
I know this is personal, but when you were young did you ever have such thresholds (weight, mobility, etc.) in mind ? Or did it just sneak up on you and by then you were in gaining weight at a surprising rate beyond your control ? No worries if you are too busy to respond. I wish you the best!